I don't believe tightening these requirements would benefit all companies as
a whole. The problems I've seen experienced are isolated to specific
designs, on specific equipment.

I would propose something more clarified in respect to customers (i.e.
assemblers) and suppliers reviewing designs more closely together. Customer
A may have equipment to handle a certain amount of warp (as noted below)
while Customer B may not, Customer B could then tighten this specific
tolerance to a certain supplier who might make adjustments for a certain
amount of additional processing or even yields.

A general tightening of bow/twist may cause acceptable product to be
scrapped that might otherwise be used if pre-fabrication including
fabrication requirements discussions were performed.

Franklin D Asbell

-----Original Message-----
From: IPC-600-6012 [mailto:[log in to unmask]] On Behalf Of John Perry
Sent: Wednesday, May 10, 2006 2:49 PM
To: [log in to unmask]
Subject: [IPC-600-6012] IPC-6012B Bow and Twist Requirements

Colleagues,

IPC continues to receive queries from industry as to whether or not
there will be a tightening of the bow and twist requirements for printed
boards that are given in both IPC-2221A and IPC-6012B.

I would like the members of this forum to provide their feedback on
these requests.

There are currently two arenas where we are getting requests for
alteration to the requirements: BGA devices and screen printing
technology.

Regarding BGA technology, Don Dupriest of Lockheed Martin Missiles and
Fire Control provided a .ppt file at the IPCWorks 2005 meeting for these
groups where the recommendation for bow and twist acceptance for
isolated BGA areas is 0.50%.

This presentation file is available at
http://www.ipc.org/committeedetail.asp?Committee=D-33A

Within "Drafts", under the titled "PCB Bow and Twist - BGA Devices"

Regarding screen printing technology, we recently received the following
request:

We had a board that was slightly warped, make contact with and damage
the camera in one of our screen printers. Of course, when I measured the
bow and twist, it was well within acceptable limits for bow and twist.

My question is this: Are the bow and twist specifications tight enough?
For over 15 years, I have been "jumped on" by the line operators and
maintenance guys to fixed warped boards only to find that the boards are
usually not any where near the limits. Since I have worked for multiple
companies, I see that this is an industry wide dilemma. Board
manufacturers typically can hold bow and twist requirements, but
different SMA machines (especially screen printers) aren't able to run a
board that has bow or twist near but within the specification limits.
Should I be asking why machines built for the surface mount industry
can't run boards that meet industry specifications, or if the
specifications that once fit, are in need of revision?

Larry D. Roberts
Quality Engineer
Andrew Corporation

Thanks for taking the time to review and respond to these industry
requests.

Regards,

John Perry
Technical Project Manager
IPC
3000 Lakeside Drive # 309S
Bannockburn, IL 60015
[log in to unmask]
1-847-597-2818 (P)
1-847-615-7105 (F)
1-847-615-7100 (Main)